In recent years, a displacement control device has been desired for adjusting an optical path length or a position by the submicron in fields of optics, precision machinery, semiconductor manufacturing, and the like. To respond to this, development has been promoted of piezoelectric/electrostrictive devices such as a piezoelectric/electrostrictive actuator utilizing strain based on the inverse piezoelectric effect, the electrostrictive effect, or the like caused when an electric field is applied to a ferroelectric body or an antiferroelectric body and a piezoelectric/electrostrictive sensor utilizing charge generation caused when stress is applied to a ferroelectric body/antiferroelectric body on the basis of a similar effect.
For example, an embodiment of a piezoelectric/electrostrictive actuator has a structure where a piezoelectric/electrostrictive actuating portion obtained by laminating a lower electrode, a piezoelectric/electrostrictive body, and an upper electrode in sequence on a surface of a ceramic substrate formed by unitarily forming a thick support portion having a cavity and a vibration portion covering the cavity. In such a piezoelectric/electrostrictive actuator, when an electric field is generated between the upper electrode and the lower electrode, a piezoelectric/electrostrictive body of a piezoelectric/electrostrictive material is deformed to generate a displacement in a vertical direction in the vibration portion. By the function of displacing the vibration portion, the piezoelectric/electrostrictive actuator is applied as an actuator portion of a precision equipment. Such a piezoelectric/electrostrictive actuator controls contact or noncontact of a switch or controls fluid as a micro pump by, for example, transforming the vibration portion vertically.
In the case that a piezoelectric/electrostrictive actuator as described above is used as an actuator portion or the like of a switch or a micro pump, when the displacement is not large enough, a stroke is insufficient in the switch, and it does not function as a switch, or a fluid extrusion amount is insufficient in the micro pump or no fluid can be extruded in some cases. In addition, for example, in the case of using a plurality of piezoelectric/electrostrictive actuators together, when the displacement is varied among the actuators, contact or noncontact motion becomes unstable, or a fluid extrusion amount becomes unstable to deteriorate quality of the switch or the micro pump.
Therefore, quality control is performed so that the displacement of each vibration portion may have at least a certain amount and be uniform when the same voltage is applied (same electric field is generated).
Incidentally, a prior art document of the same technical field is a WO No. 05/104258 pamphlet.
An example of a testing method performed when piezoelectric/electrostrictive actuators are shipped as products is a method for directly testing the displacement of the vibration portion by the use of a laser Doppler vibrometer or the like. In addition, there has been known a method for testing the size and uniformity of the displacement when the same voltage is applied (same electric field is caused) by measuring capacitance of a piezoelectric/electrostrictive body to be used to resemble a condenser in a manufacturing step of a piezoelectric/electrostrictive actuator.
However, the former method requires high costs when the test is performed for all the lots of the piezoelectric/electrostrictive actuators manufactured. In addition, the latter method does not always have high testing precision because the constituents other than the piezoelectric/electrostrictive actuating portion of the piezoelectric/electrostrictive actuator are not reflected to the test.
Further, in a recent piezoelectric/electrostrictive actuator, because of the advance of miniaturization, slight slippage or variance of the size more seriously influences on the properties, and observation of a cross section with the destruction is necessary to test the slippage or variance of the size. In such a case, it is impossible to directly test the products to be shipped.
Such a problem is likewise caused also in a piezoelectric/electrostrictive sensor where the uniform sensor sensitivity is required in the case of the same design and specification.